In the medical field, implantable medical electrical leads are used with a wide variety of medical devices. For example, implantable medical electrical leads are commonly used to form part of an implantable medical system that provides therapeutic electrical stimulation to a patient, such as cardiac electrical stimulation to the heart in the form of pacing, cardioversion, defibrillation, or resynchronization pulses. The pulses can be delivered to the heart or other desired location within the patient via electrodes disposed on the leads, e.g., typically near distal ends of the leads. In that case, the leads may position the electrodes with respect to various locations so that the implantable medical system can deliver pulses to the appropriate locations. Leads are also used for sensing purposes, or for both sensing and stimulation purposes. Implantable leads are also used in neurological devices to deliver electrical stimulation to reduce the effects of a number of neurological disorders and in a number of other contexts.
Patients that have implantable medical systems may benefit, or even require, various medical imaging procedures to obtain images of internal structures of the patient. One common medical imaging procedure is magnetic resonance imaging (MRI). MRI procedures may generate higher resolution and/or better contrast images (particularly of soft tissues) than other medical imaging techniques. MRI procedures also generate these images without delivering ionizing radiation to the body of the patient, and, as a result, MRI procedures may be repeated without exposing the patient to such radiation.
During an MRI procedure, the patient or a particular part of the patient's body is positioned within an MRI device. The MRI device generates a variety of magnetic and electromagnetic fields to obtain the images of the patient, including a static magnetic field, gradient magnetic fields, and radio frequency (RF) fields. The static magnetic field may be generated by a primary magnet within the MRI device and may be present prior to initiation of the MRI procedure. The gradient magnetic fields may be generated by electromagnets of the MRI device and may be present during the MRI procedure. The RF fields may be generated by transmitting/receiving coils of the MRI device and may be present during the MRI procedure. If the patient undergoing the MRI procedure has an implantable medical system, the various fields produced by the MRI device may have an effect on the operation of the medical leads and/or the implantable medical device (IMD) to which the leads are coupled. For example, the gradient magnetic fields or the RF fields generated during the MRI procedure may induce energy on the implantable leads (e.g., in the form of a current), which may be conducted to tissue via the electrodes of the lead.